The invention relates to microarraying and spotting, more especially but not exclusively to microarraying apparatus and to pin heads for microarraying apparatus.
Microarraying is a technique in widespread use in fields such as chemistry and biotechnology. Liquid samples are stored in the wells of a well plate. The liquid may be assays or any other biological or chemical sample of interest. To spot the liquid from a well, a pin is dipped in the well to retrieve an amount of the liquid. The pin carrying an amount of the liquid is then moved across to a spotting surface of a microscope slide or other suitable surface. A spot of liquid is deposited on the slide by bringing the pin into close proximity with the slide surface, or by physically contacting the tip of the pin with the slide surface.
In general, a plurality of slides and well plates are arranged on a surface of a microarraying apparatus. An array of pins is held in a pin holder which is mounted on a frame above the arraying surface. A motorized positioning system is provided to move the pin holder laterally about the frame so that the pins can be moved between the slides and well plates, and other areas such as a wash station. A vertical positioner or drive is also provided for causing vertical motion of the pins. This allows the pins to be dipped into the well plates and also allows the pins to be brought into contact with the slides for spotting.
Typically, microarraying apparatus of this type are large and costly pieces of equipment intended for large scale use, and are capable of handling a large volume of well plates and slides. Given the repetitive nature of the spotting procedure and the large lateral distances between the well plates and spotting surfaces of the slides, the vertical pin drive is required to have the capability of returning exactly to any desired absolute height position many thousands or tens of thousands of times without any long term drift.
For example, the pin drive must be able to dip the pins into the wells to a suitable depth to pick up liquid, and also to deposit the liquid as desired on a spotting surface. Spotting requires that the pin or pins approach the spotting surface with great precision, in order to be close enough for effective deposit of the liquid without the pin crashing into the slide. In other words, attaining an appropriate clearance height during spotting is critical, and must take account of factors such as use of slides of different thicknesses. Similarly, well plates may be of different thicknesses or have reservoirs filled to different levels.
To attain the necessary specification, the pin drive is typically provided with some kind of height sensing with feedback, such as an interferometric encoder system. Although precision feedback systems for accurate height sensing are effective and available with established technology, they are costly, and contribute substantially to the overall cost of a microarraying apparatus.
While cost is not a major factor for high volume applications, it is a considerable deterrent to the more widespread use of microarraying for smaller scale research projects.
The invention is based on the realization that feedback control for the pin drive becomes unnecessary if one instead prealigns the relative heights of the spotting surface and the well plates such that the pins in the pin head can be lowered to the same absolute height both for picking up liquid from the well plates and depositing it onto the spotting surface. By aligning the heights of the well plates relative to the spotting surfaces, the pin drive needs only to be able to reproducibly and accurately arrive at a single lowered position. Building from this realization, it has been further appreciated that a pin head can be designed to achieve this functionality purely with a mechanically defined bottom point, obviating the need for an encoder or other feedback control system for height determination of the pins. Moreover, it is a simple matter to provide a height adjustable platform for supporting the area carrying the well plates, or alternatively a height adjustable platform for supporting the area carrying the microscope slides for spotting onto. Through these measures it becomes possible to produce a microarraying apparatus of significantly reduced cost that can be used for small-scale experimentation.
Accordingly, a first aspect of the invention is directed to a pin head for a microarraying apparatus comprising: a pin holder for carrying an array of pins; a vertical drive operable to move the pin holder in a vertical axis; and a positioning mechanism that cooperates with the vertical drive to mechanically define a lowest point of travel for the pins in the vertical axis.
Moreover, a second aspect of the invention is directed to a microarraying apparatus comprising: an apparatus bed defining an arraying surface for carrying one or more slides; a well plate platform for carrying at least one well plate; and a height adjustment mechanism operable to alter the height of the well plate platform relative to that of the apparatus bed.
In use, the microarraying apparatus is aligned before use using the height adjustment mechanism, which is preferably manually actuatable for simplicity and cost reasons. Alignment is achieved by ensuring that the horizontal plane defined by the lowest point of travel of the pins lies an appropriate distance below the surface of the liquid held in the well plates and an appropriate distance above the spotting surface of the slides (which may be zero in the case of near-contact of the pin tips with the spotting surface).
The pin holder has simple vertical motion with a defined lowest position in which the pin holder can be readily located without the need for complex encoder systems. This arrangement permits a microarraying apparatus to be set up with its component parts positioned correctly with respect to the position of the pins when the pin holder is in the lowest position, so that spotting can be carried out without the need for control of the vertical position of the pins during the spotting process.
For some applications where pins are individually fired to the bottom position, the vertical drive may be connected directly to the pins rather than via the pin holder in which case there may be provided a pin head for a microarraying apparatus comprising: a pin holder carrying an array of pins; a vertical drive operable to actuate the pins in a vertical axis individually or collectively; and a positioning mechanism that cooperates with the vertical drive to mechanically define a lowest point of travel of the actuated pins in the vertical axis.
Advantageously, the positioning mechanism comprises a crank system having a bottom dead center and coupled to the pin holder so that the pin holder achieves its lowest position when the crank system is at bottom dead center. A crank system is a simple way of limiting the travel of the pin holder to define the lowest position. Also, the operation of a crank system means that the pin holder and pins therein move at very low velocity and acceleration as the crank system approaches bottom dead center, reaching a momentary static point at the lowest position even if the crank is continuously rotated. This smooth pin approach is highly desirable for ensuring good quality spots are deposited.
The vertical drive may comprise a rotary solenoid or a rotary motor which is coupled to the pin holder by the crank system, the crank system operable to transfer motion produced by the rotary solenoid to the pin holder. A rotary solenoid has the advantage of only requiring a very simple on/off actuation signal. For example, the bottom position may be associated with a deenergized state of the solenoid and a withdrawn position associated with an energized state of the solenoid (or vice versa).
Another aspect of the present invention is directed to a head apparatus combining the above described pin head with an additional height adjustment mechanism. More especially, the head apparatus comprises: a mount adapted to attach a pin head to a microarraying apparatus; a pin head as described above movably mounted on the mount; and a pin head height adjustment arrangement operable to allow the lowest position of the pins to be varied relative to the mount.
A still further aspect of the present invention is directed to a microarraying apparatus comprising: an arraying surface; a slide holder for holding one or more slides mounted on the arraying surface; a well plate platform for holding one or more well plates mounted on the arraying surface; and a platform height adjustment mechanism operable to alter the relative heights of the slide holder and the well plate platform.
The platform height adjuster may be provided with a distance scale which is indicative of the difference in the relative heights of the slide holder and the well plate platform.
The platform height adjuster facilitates setting up the apparatus so that the slides and well plates are at heights at which dipping and spotting can be performed with the same lowest vertical pin position.
It will be appreciated that further height adjustable platforms may be provided, for example for a wash station, so that pins are dipped into cleansing liquid in the wash station to a sufficient depth for cleaning.
The microarraying apparatus may further comprise a mounting frame mounted over the arraying surface; and a pin head mounted on the mounting frame. The pin head is provided with a drive system operable to move the pin head in a plane parallel to the arraying surface. The pin head comprises a pin holder for holding an array of pins, a vertical drive operable to move the pin holder along a vertical axis, and a positioning mechanism which defines a furthest point of travel of the pin holder along the vertical axis, the furthest point being the lowest position achievable by the pin holder.
In this way, a simple pin head which has a repeatable lowest position can be used for dipping and spotting. Specifically, precision, accuracy and reproducibility are achievable without the need for a feed-back-controlled pin head, since the pin head is only required to be able to find its bottom position precisely, accurately and reproducibly, which can be performed with a variety of simple mechanical or electromechanical solutions.
A still further aspect of the invention is directed to a spotting method using a microarrayer having an apparatus bed and a well plate platform, the method comprising:
arranging at least one slide on the apparatus bed to provide a spotting surface;
arranging a well plate filled to a level with spotting liquid on the well plate platform;
vertically aligning the well plate platform relative to the apparatus bed so that the spotting surface lies at a desired height at or below the level of the spotting liquid;
dipping a pin from a pin head into the spotting liquid by moving the pin to a lowered position;
moving the pin head across the microarrayer to a spotting position; and
depositing the spotting liquid onto the spotting surface by moving the pin once again to the lowered position.